Prunetune was a famous tupo made by the founder of Candy Crush Saga Wikia, Lefty7788, around October 2014. The word he meant to type was "Primetime", a bureaucrat on the before-mentioned Wikia, and was instructing him to check PM.
The tupo was brought about as the "U" and "N" keys are to the left of "I" and "M", thus Lefty typed those letters out wrong accidentally.
The tupo quickly rose to fame as people found it hilarious. The tupo was so big that Primeitme himself changed his aka from "THE historian" (which it had been for months), to "Prunetune".
Many people still call him Prunetune today.